1. Field of the Art
This invention relates to a catheter type ultrasound probe to be inserted into an intracavitary portion of a patient to make intracorporeal examinations by ultrasound scanning.
2. Description of the Prior Art
There have been known in the art the so-called catheter type ultrasound examination systems having an ultrasound transducer mounted on a tip end of a catheter member to be inserted into an intracavitary portion of a patient, to obtain a tomographic ultrasound image of a particular intracorporeal portion of interest by an ultrasound scanning operation moving the ultrasound transducer in a linear direction or in a rotational direction about the axis of the catheter member. The ultrasound internal examination systems of this sort are largely constituted by an elongated catheter member to be introduced into an intracavitary portion directly or indirectly through a guide means on an endoscope or the like, and a controller section with manipulating means to control the position of the transducer for the ultrasound scanning operation. In certain cases, a catheter member is integrally connected to a controller section. However, there are also separate type catheter members which are disconnectibly connectible to a controller section prior to use.
For the purpose of protecting the ultrasound transducer which is mounted on a distal end portion of the catheter member, it is the usual practice in the art to encase the catheter member in a sheathing in the form of a flexible tube, which has its distal end simply closed or closed with a closure cap with excellent acoustic properties, and to mount an ultrasound transducer on a cradle-like support plate within a fore end portion of the sheathing tube. In case of radial scanning, the ultrasound transducer is rotationally driven within the sheathing tube. In order to put the ultrasound transducer in rotation, the support plate which supports the transducer needs to be rotatable and connected to a rotation transmission member which is extended through the catheter member to the proximal end thereof. In case the catheter member is of the type which is integrally connected to the controller, the rotation transmission member is further extended into the controller and coupled with a rotational drive means such as electric motor or the like. On the other hand, in case the catheter member is of the separate type as mentioned above, the rotation transmission member is extended to a rotational coupling means at the proximal end of the catheter member, which is disconnectibly connectible to a drive source on the part of the controller. As far as the linear scanning operation is concerned, there is no need for driving the ultrasound transducer from the rotational drive source while the transducer is in a linear scanning operation. However, in order to control the angular position of the ultrasound transducer, it is necessary to provide a rotation transmission member which can turn the ultrasound transducer into a desired angular position prior to a linear scanning operation.
On the other hand, the catheter member should be capable of bending itself in an arbitrary direction along a path of insertion leading to an intracavitary portion to be examined. The sheathing tube of the catheter member, which is formed of a flexible material, can bend itself along turns or bends in the path of insertion. In this regard, the rotation transmission member which is encased in the flexible sheathing tube should also have a suitable degree of flexibility. This requirement for the rotation transmission member can be suitably met by a flexible shaft which is constituted by a transmission coil or coils each consisting of a series of tightly contacting helices in the longitudinal direction thereof.
In order to transmit rotation accurately to the ultrasound transducer by the use of a rotation transmission member in the form of such a flexible shaft or the like, it is necessary to provide a certain degree of dimensional differential between the inside diameter of the sheathing tube and the outside diameter of the rotation transmission member to reduce to a minimum the friction resulting from the sliding contact between these two parts. No matter whether the catheter member is introduced into an intracavitary portion by direction insertion or by indirect insertion, for example, under the guidance of a biopsy channel of an endoscope, it is invariably required to bend its body along a path of insertion. When the catheter member is bent into a loop-like form, for example, the rotation transmission member within the sheathing tube is forced into a deviated position to abut against the inner periphery of the sheathing tube on the inner side of the loop. This deviation of the rotation transmission member tends to shift the position of the trandsucer support plate, moving same in a direction axially forward of the sheathing tube. As a result, the ultrasound transducer is pressed against the distal end face of the sheathing tube and forcibly rotated in frictional sliding contact with the sheathing tube. This frictional sliding contact with the sheathing tube is impedimental to smooth rotation of the ultrasound transducer and has possibilities of causing irregularities in rotational movement of the transducer especially in radial scanning operations.
To cope with this problem, prior art ultrasound probes usually have the fore distal end of the sheathing tube extended axially forward beyond the position of the ultrasound transducer within the sheathing tube in a sufficient degree for keeping the transducer and its support member out of contact with the interior surfaces of the sheathing tube even when the catheter member is bent into an arcuate shape. In this connection, it should be considered that the catheter members of ultrasound probes generally have a lengthy body ranging from about 1 m to about 2.5 m in length depending upon the position of the intracorporeal portion to be examined. Therefore, even if the dimensional differential between the inside diameter of the sheathing tube and the outside diameter of the rotation transmission member is held to a minimum value which would not impair smooth rotation, it is necessary to locate the ultrasound transducer normally in a retracted position at a distance of more than 10 mm and, on the safe side, more than 20 mm from the fore distal end of the sheathing tube when the catheter member is in a rectilinearly stretched state.
However, in case the catheter member is arranged to have the fore distal end of the sheathing tube extended forward largely beyond the position of the ultrasound transducer, difficulties are often encountered in making a scan along an intracavitary wall of complicate configuration where the fore end of the sheathing tube is very likely to come into abutment against a rising portion of the intracavitary wall, which blocks the scanning of the intracavitary wall portions between the fore end of the protruded sheathing tube and the retracted mount position of the ultrasound transducer. Besides, in case the catheter member is introduced into an intracavitary portion through a biopsy channel of an endoscope, the ultrasound probe needs to be manipulated with the aid of images of the endoscopic observation system in positioning the ultrasound transducer in face to face relation with an intracorporeal portion to be examined by the ultrasound probe. However, on such an occasion, what one can see through the endoscopic observation mechanism is simply the outer configuration of the fore end of the sheathing tube protruded out of the biopsy channel, failing to check the exact position of the ultrasound transducer within the sheathing tube. For this reason, if the ultrasound transducer position is easily shifted in the axial direction within the sheathing tube, it becomes difficult to locate the transducer correctly in face to face relation with an intracorporeal portion to be examined by the ultrasound probe, or to grip the exact position of an intracorporeal portion which is being examined.